A device to device (device to device, D2D) direct link eliminates a need for transmitting data via an access point, and avoids a delay caused by network congestions. For instance, in a wireless local area network (wireless local area network, WLAN), a station usually performs communications with other stations or networks via an access point. Even for stations within a same basic service set (basic service set, BSS), data communications therebetween also need to be forwarded via the access point, that is, a transmitting station transmits data to an access point first, and then the access point forwards the data to a receiving station. When the two stations are so close that data transmission/reception may be performed directly, the forwarding via the access point then will reduce system efficiency.
In order to solve this problem, a tunneled direct-link setup (tunneled direct-link setup, TDLS) mechanism is introduced. A main setup process of the TDLS is as follows.
When a station (an initiating station) sets up a TDLS link with another station (a responding station) in a same basic service set, the initiating station will first transmit a TDLS link setup request frame to the responding station via an access point. If the responding station agrees to set up the TDLS link, then it replies a TDLS link setup response frame to the initiating station via the access point, and indicates a successful setup in the response frame. After receiving the TDLS link setup response frame with a success indication, the initiating station will transmit an acknowledgment frame to the responding station via the access point so as to indicate acknowledgement of the TDLS link setup. After the TDLS link is set up, data transmission and reception may be performed between the initiating station and the responding station directly (that is, a D2D direct link is set up between the transmitting station and the responding station).
A power saving mechanism is supported in a current TDLS mode. In this mechanism, when a station in the TDLS has data to be transmitted to a receiving station, and the receiving station is in a sleep state, a transmitting station of the data will transmit an indication frame to an access point, and then the indication frame is forwarded by the access point to the receiving station. After receiving the indication frame, the receiving station transmits a response frame to the transmitting station, and then waits for the data transmitted by the transmitting station.
Reference may be made to FIG. 1 for a brief process for supporting the power saving mechanism, where a station 1 and a station 2 have set up a TDLS link successfully, and the station 2 is in a power saving state, whereas the station 1 has buffered data needing to be transmitted to the station 2. A transmitting process is as follows:
Step 1: a station 1 transmits a TDLS Peer Traffic Indication frame (reference may be made to Table 1 for a structure of the TDLS Peer Traffic Indication frame) to an access point;
TABLE 1Element sequenceElement nameRepresentation1Typeused to indicate that the type isTDLS2Actionused to indicate that the actionis TDLS Peer Traffic Indication3Dialog Tokenusing an integer character torepresent a dialog process of TDLSPeer Traffic Indication and TDLSPeer Traffic Response4Link identifierused to indicate the TDLS link,including a BSSID, addresses ofa TDLS initiating station and aTDLS responding station5PTI controlThis item is optional, which isused to indicate a TID and asequence number of a last MPDUtransmitted to a target powersaving station via the TDLS link6TPU buffer statusused to indicate an access typeof buffered data
Step 2: the access point forwards the TDLS Peer Traffic Indication frame to a station 2;
Step 3: after receiving the TDLS Peer Traffic Indication frame, the station 2 transmits a TDLS Peer Traffic Response frame (reference may be made to Table 2 for a structure of the TDLS Peer Traffic Response frame) to the station 1 via the TDLS link directly, and meanwhile maintains a waking state;
TABLE 2Element sequenceElement nameRepresentation1Typeused to indicate that the type is TDLS2Actionused to indicate that the actionis TDLS Peer Traffic Response3Dialog Tokenusing an integer character torepresent a dialog process of TDLSPeer Traffic Indication and TDLSPeer Traffic Response4Link identifierused to indicate the TDLS link,including a BSSID, addresses of aTDLS initiating station and a TDLSresponding station
Step 4: the station 1 transmits data to the station 2;
It can be seen from setup of the TDLS that: during setup of a D2D direct link, if a receiving station is in a sleep state, then an access point needs to transmit an indication frame to the receiving station specially, and when a plurality of direct links need to perform data transmission, the access point needs to unicast an indication frame for each receiving station respectively, thereby resulting in larger signaling overheads during setup of data links.